This invention relates to an apparatus for the manufacture of a fibrous web, which apparatus includes a fiber distributor comprising a housing having inlet means for a dry, defibrated fibrous material and a perforated bottom wall, and stirring means including impellers which are rotatably mounted within the housing; an air-permeable forming wire; means for advancing the wire in a path located a short distance below the bottom wall of the fiber distributor; and a suction box mounted below the fiber distributor and the forming wire.
A prior art apparatus for the production of a fibrous web comprises several fiber distributors and corresponding suction boxes mounted at intervals along a forming wire. When using such an apparatus, the thickness of the fibrous web formed is increased stepwise. However, fibrous products which are made stepwise tend to delaminate because of an insufficient integration between adjacent fiber layers. Consequently, a relatively large amount of binder is required to obtain a desired strength of the final fibrous product. Furthermore, this prior art method of manufacturing fibrous products presents serious problems when light weight products are desired. In that case, the fibrous layer initially deposited on the forming wire is very thin and consequently is easily damaged when passing through the zone between two adjacent fiber distributors, i.e., because it is merely loose on the wire within such zone. Furthermore, in case of very thin products in which the fibers are not entangled in one another, the fibers tend to form groups of fibers during the passage between two fiber distributors and, therefore, non-uniform products are obtained. This problem becomes aggravated when the speed of the forming wire is increased to increase the production rate.
In order to prevent the introduction of false air at the front and rear edges of the fiber distributors and consequently a non-uniform distribution of fibers in the fiber layers formed, driven rollers contacting the forming wire or the fiber layer deposited thereon have been mounted at each fiber distributor.
The use of such rollers presents the drawback that the fibers, unless their moisture content is maintained within narrow limits, tend to accumulate on the surfaces of the rollers and form layers thereon. Furthermore, such rollers tend to increase the tendency of delamination of the fibrous product formed because they smooth out the surface of the fiber layer formed and consequently prevent fiber ends extending from the layer from being entangled with fibers of a fiber layer subsequently applied.
The object of the present invention is to provide an apparatus which is capable of producing an improved uniform fibrous web. A further object is to produce a strongly coherent fibrous product at a high production rate